Transcription and translation of the sex message in the smut fungus Ustilago violacea. II. The effects of inhibitors.

In Ustilago violacea conjugation involves a period of courtship followed by the cooperative assembly of a conjugation tube between paired sporidia of opposite mating type. During courtship information is exchanged between the paired sporidia directing transcription and translation of a ' sex message'. This information exchange is completed even though the plasma membranes and walls of the mating sporidia remain intact until after the sex message has been translated. Once translation is completed the copulatory organelle is assembled. Inhibitor studies show that translation of specific mRNA species (sex message) is essential during the 3-4 h period of courtship prioi to assembly and that transcription of this sex message is completed 15-30 min prior to the completion of translation. Amino acid incorporation studies show that even though the cellular protein levels remain constant during courtship there is extensive amino acid turnover as the sporidia adjust to mating conditions. However, an enhancement of amino acid turnover by mating, in contrast to unmixed sporidia, is not detectable. Prototrophic strains continue to synthesize stable RNA during courtship while amino acid auxotrophs discontinue stable RNA synthesis immediately on transfer to mating conditions. Both prototrophs and auxotrophs show extensive RNA turnover during courtship but a specific enhancement of turnover due to mating activity is not detectable from the labelling pattern alone. A lound of DNA replication may be completed during courtship but mating activity does not influence the gross pattern of DNA replication in either of the mating types.